The present invention relates to a shift system adapted to shift an automatic transmission of a passenger vehicle, and more particularly relates to an electronic modular unit adapted to attach to a casing of an existing transmission and that is adapted to shift the transmission based on electronic inputs.
Traditional automatic transmissions for passenger vehicles include an actuator rod or "D rod" that extends from the transmission and that can be rotated to different angular positions to shift the transmission between gear positions, such as park, reverse, neutral, and drive. Historically, the actuator rod is controlled by manually manipulating a shifter in the passenger compartment of the vehicle, with the shifter being operably connected to the actuator rod by a mechanical linkage, such as a telescoping Bowden cable or a rigid rod. Many vehicle manufacturers desire to change from the mechanical linkage to an electronically controlled shifting arrangement. One reason is to eliminate assembly problems associated with routing and connecting a stiff Bowden cable or rigid linkage between the shifter and the transmission. Another reason is to take advantage of wiring, which is easier to route and connect, requires less space, is more flexible, and is more forgiving of product variation. Also, wiring does not require a large passageway through the vehicle floor pan or firewall, thus reducing the noise and environmental problems (e.g., corrosion, water leaks, etc.) associated with large passageways through or holes in the floor pan or firewall. Also, more and more manufacturers are incorporating electrical components and electronically controlled systems into vehicles in order to take advantage of advancements in electronics for improved vehicle control, in order to meet customer demands and in order to achieve cost savings.
Despite the advantages of an electronic shifting system, another problem is that manufacturers have already made large investments in existing transmission designs and in the related tooling, fixturing, and manufacturing operations. It would require substantial lead time and huge new capital investments in order to redesign, tool up, and begin producing transmissions that are adapted to be shifted entirely and solely by an electronic signal. Thus, a system that is retrofittable and/or useable on or with existing transmissions is desired.
At least one manufacturer is considering using a DC motor attached to the actuator rod of an existing transmission to selectively rotate the actuator rod between gear positions. However, there are problems and disadvantages associated with using a DC motor in the harsh environment under a vehicle, since DC motors are not well suited for harsh environments since DC motors tend to be relatively complex and high warranty. For example, DC motors include brushes and rotating armature windings. Further, DC motors tend to be heavier and larger than desired, which can be problematic given today's stringent gas mileage requirements for vehicles. Further, space is always a problem, particularly with front wheel drive vehicles where both the motor and the transmission are located at a front of the vehicle. Another problem with DC motors is their relatively slow response time, their low torque per unit weight, and their relatively high current usage and requirements. Further, DC motors require a separate detent to hold them in a selected position after being moved, which results in extra parts and a more complicated assembly.
In addition to the above, vehicle manufactures are considering replacing traditional hand-operated shift levers, and instead using different driver interface modules (e.g. pushbuttons, miniaturized control levers or joysticks, and the like) for receiving driver inputs to control shifting transmissions. It is important that whatever interface module is used, the shifting system must be able to incorporate the same.
Accordingly, a simplified yet durable electronic shifting system for shifting existing transmissions is desired that solves the aforementioned problems and that has the aforementioned advantages.